﻿<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>判断方法是否已经定义2</title>
    <script LANGUAGE="JavaScript">
        if(typeof a!='function'){
            alert("方法a没有定义！");
        }
    </script>
</head>
<body>

</body>
</html>